Hello Tony Dean
SpaceClaim is a direct modeling tool whereas most of the other CAD tools are feature based. In feature based CAD tools, a dimension is automatically associated with the sketch and you can edit it by clicking the dimension box. In Spaceclaim, this functionality of feature base tool is now provided in the form of Dimensions tool wherein you can define a dimension for the sketch and then modify it as required.
Can you let me know which tutorial video are you referring to so that I can also check it out?